1. Field of the Invention
The invention relates to a liquid submerged portion fuel leakage diagnostic apparatus that diagnoses the presence or absence of leakage of fuel from a liquid submerged portion of a fuel tank for an internal combustion engine, the liquid submerged portion being submerged in fuel in the fuel tank, and the fuel tank being connected to a canister via a vaporized fuel passage, and being configured such that an is internal space thereof is able to be hermetically closed by a block valve provided in the vaporized fuel passage.
2. Description of Related Art
There is known a technique in which, during a stop of an internal combustion engine, a vaporized fuel treating mechanism for an internal combustion engine which includes a fuel tank is depressurized by a pump, and the presence or absence of leak from the vaporized fuel treating mechanism is diagnosed on the basis of change in the internal pressure in a path during the pressure reduction (see, e.g., Japanese Patent Application Publication No. 2006-170074 (JP 2006-170074 A)).
There have been proposed a system that performs the aforementioned fuel vapor leak diagnosis on the basis of the presence or absence of change in the fuel liquid surface height in a fuel trapper (see, e.g., Japanese Patent Application Publication No. 2010-270618 (JP 2010-270618 A)) and a system that performs correction of data used for fuel vapor leak determination on the basis of the value indicated by a level gauge that detects the fuel liquid surface (see, e.g., Japanese Patent Application Publication No. 2004-270573 (JP 2004-270573 A)).
The leak diagnostic technologies described in the aforementioned publications JP 2006-170074 A, JP 2010-270618 A and JP 2004-270573 A are the same in that leakage of fuel vapor present in an upper space above the fuel liquid surface in the fuel tank is detected on the basis of change in pressure.
As for the fuel leakage, fuel can sometimes leak from a region below the fuel liquid surface in the fuel tank, that is, from a liquid submerged portion of the fuel tank. Such leakage from the liquid submerged portion is leakage of liquid. Unlike leakage of gas, leakage of liquid does not readily manifest itself as a change in the pressure in the upper space above the fuel liquid surface.
Therefore, the fuel leakage from the liquid submerged portion cannot be detected by the leak diagnostic systems as described in JP 2006-170074 A, JP 2010-270618 A and JP 2004-270573 A, so that a suitable diagnostic device has been required.